The present invention relates to semiconductor circuits, and more particularly to integrated circuit packaging and to vertical integrated circuits.
Integrated circuits are typically attached to a wiring substrate, for example, a printed circuit board (PCB), for easy connection to other circuits. Attachment can be done using flip-chip technology. According to this technology, conductive bumps are formed on the contact pads of the chip (die) incorporating the circuit. The bumps can be made by growing solder on the contact pads or by electroplating gold or some other material. Then the chip is bonded with its bumps to the wiring substrate.
Sometimes, the contacts on the wiring substrate cannot be made with the same precision as the contacts on the chip. For example, typical PCB fabrication technology is not as precise as semiconductor fabrication technology used for chip fabrication. Therefore, the chip contacts have to be made larger, and spaced farther from each other, to accommodate PCB fabrication technology.
Another reason why the chip contacts cannot be made as dense as allowed by the semiconductor fabrication technology is large tolerances required by many bumping processes.
This problem is exacerbated by the fact that the chip contacts placement is sometimes restricted by the layout of the chip circuitry. For example, many chips have their contacts restricted to the peripheral area. This makes it more difficult to accommodate larger widely spaced contacts as required by the PCB technology and bumping processes.
Therefore, sometimes a chip is bonded to a molded plastic substrate, which is bonded to the PCB. The plastic substrate can be larger than the chip, or it can have the same size. On the plastic substrate, the position of the contacts bonded to the PCB is not as limited as on the chip. For example, the contacts can be evenly distributed on the plastic substrate's surface bonded to the PCB (so-called "area matched package").
Alternative packaging techniques are desirable.